Bio 112: Virus

What is the basic structure of a virus?

A virus consists of nucleic acid surrounded by a protein coat.

What defines a virus as an infectious particle?

A virus is defined as an infectious particle consisting of genes packaged in a protein coat.

Are viruses considered living organisms?

The question of whether viruses are living is a subject of debate.

What are viruses unable to do outside of a host cell?

Viruses cannot reproduce or carry out metabolism.

How are viruses classified in terms of life-forms?

Viruses exist in a shady area between life-forms and chemicals, leading to a concept of 'borrowed life'.

What disease did the discovery of viruses begin with?

Tobacco mosaic disease, which stunts growth and causes mosaic coloration in tobacco plants.

What did researchers initially hypothesize was responsible for tobacco mosaic disease?

Unusually small bacteria.

Who confirmed the existence of viruses by crystallizing the infectious particle in 1935?

Wendell Stanley.

What types of nucleic acids can viral genomes consist of?

Double or single-stranded DNA or RNA.

What are the two classifications of viruses based on their genetic material?

DNA viruses and RNA viruses.

What is a capsid?

The protein shell that encloses the viral genome.

What are capsomeres?

Protein subunits that make up a capsid.

What are bacteriophages?

Viruses that infect bacteria.

What is the difference between the lytic and lysogenic cycles of phages?

The lytic cycle culminates in the death of the host cell, while the lysogenic cycle replicates the phage genome without destroying the host.

What is a virulent phage?

A phage that reproduces only by the lytic cycle.

What is a temperate phage?

A phage that can use both the lytic and lysogenic cycles.

What is a prophage?

Integrated viral DNA within the host cell's chromosome during the lysogenic cycle.

How do bacteria defend against phages?

By evolving surface proteins that phages cannot recognize and using restriction enzymes to cut foreign DNA.

What are the two key variables used to classify animal viruses?

The type of genome (RNA or DNA) and the presence or absence of a membranous envelope.

What is a retrovirus?

A virus that uses reverse transcriptase to copy its RNA genome into DNA.

What is the viral DNA integrated into the host genome called?

A provirus.

What is the function of RNA polymerase in the context of proviruses?

It transcribes proviral DNA into RNA molecules for viral protein synthesis and as genomes for new virus particles.

What is an example of a retrovirus that causes a significant disease?

HIV (human immunodeficiency virus), which causes AIDS.

What role do viral glycoproteins play in viral infections?

They bind to specific receptor molecules on the surface of a host cell.

What happens to the viral envelope during the exit of the virus from the host cell?

It is usually derived from the host cell's plasma membrane.

What is the significance of the herpesvirus in relation to viral envelopes?

It is an example of a virus that acquires its envelope from the host's nuclear envelope and Golgi apparatus.

What is the main question regarding the classification of viruses?

Are viruses considered alive?

What are the seven functions of life?

Respiration, reproduction, response to stimuli, growth, movement, excretion, nutrition.

What are some characteristics of viruses that classify them as non-living?

Not made of cells, do not breathe, require a host cell to reproduce, do not accumulate or release waste, do not store or obtain energy.

What are some characteristics of viruses that indicate they are alive?

Can reproduce, can move, respond to stimuli, have genes & DNA/RNA.

What is the evolutionary origin of viruses?

Viruses probably evolved as bits of cellular nucleic acid, with candidates for their genomes including plasmids and transposons.

What is the size of the largest identified virus?

The largest virus identified is the size of a small bacterium.

What are prions?

Infectious proteins that cause degenerative brain diseases in animals.

How do viruses damage or kill cells?

By causing the release of hydrolytic enzymes from lysosomes or producing toxins that lead to disease symptoms.

What is the purpose of a vaccine?

A harmless version of pathogenic microbes that stimulates the immune system to mount defenses against harmful pathogens.

Can viral infections be treated with antibiotics?

No, viral infections cannot be treated by antibiotics.

What are emerging viruses?

Viruses that suddenly become apparent, such as HIV and COVID-19.

What are some causes of rapidly emerging viral diseases in humans?

Mutation of existing viruses, spread from small isolated populations, and spread from other animals.

What is the significance of the H5N1 strain of influenza?

It is deadly and different from circulating strains, making it hard for people to mount an immune response.

What is the origin of the H1N1 strain known as swine flu?

It is a unique combination of swine, avian, and human influenza genes, not directly transmitted from pigs.

What are the two major routes of plant virus transmission?

Horizontal transmission through damaged cell walls and vertical transmission from parent to offspring.

What diseases are caused by prions?

Scrapie in sheep, mad cow disease, kuru, and Creutzfeldt-Jakob disease in humans.

How do prions propagate?

By converting normal proteins into misfolded versions and aggregating into complexes.

What is the role of environmental changes in the spread of emerging viruses?

Changes such as new roads or climate change can increase the spread of viruses.

What are the characteristics of most plant viruses?

Most have an RNA genome and can have either a helical or icosahedral capsid.

What is the estimated origin of about three-quarters of new human diseases?

They originate from existing viruses that spread from animals.

What is the significance of the influenza A virus?

It infects a wide variety of animals and is responsible for flu epidemics.

How do influenza viruses generate new genetic combinations?

They have nine RNA segments in their genome and a high rate of mutation.

What is the relationship between seasonal flu viruses and emerging viruses?

Normal seasonal flu viruses are not considered emerging but still undergo mutation and reassortment.

What are some examples of viral diseases affecting plants?

Diseases that cause spots on leaves, stunned growth, and damaged flowers or roots.

What is the controversy surrounding the evolution of large viruses?

It is debated whether they evolved before or after cells.

What is the role of antiviral drugs in treating viral infections?

They help to treat viral infections by inhibiting viral DNA synthesis and interfering with assembly.